Earlier this week, I found out I have a Vitamin D deficiency. A resident of Beijing, I only recently tried to figure out what was going on after symptoms of fatigue and mild depression led me to the doctor, who ordered a series of blood tests. He told me I was among a number of expats who become Vitamin D deficient after moving here. We deduced that the lack of sunshine from the pollution cover and the fact that I stay inside more often because of air quality issues led to my deficiency. Luckily, the fix is easy: my doctor prescribed a large dose of daily Vitamin D supplements. But it made me wonder how, after only a year and a half of living in China, Beijing’s poor air quality has already affected my health. As it turns out, I’m not the only one, when it comes to a Vitamin D deficiency. A recent study conducted by seven Chinese hospitals across five cities found that more than half of the Chinese population suffers from the same problem. The study measured vitamin levels in more than 2,000 volunteers and found that only about 5% of participants had healthy levels of Vitamin D, which is crucial for strong bones and a healthy immune system. That’s compared to about 67% of the U.S. population whose Vitamin D levels are deemed sufficient, according to a 2011 Centers for Disease Control and Prevention report.